Food container having an inner protecting layer

ABSTRACT

A food container includes: a container body made of paper, and having an inner surface defining a receiving space therein, and an outer surface opposite to the inner surface; and an inner protecting layer coated on the inner surface and made from a biodegradable coating composition including polybutylene succinate as a major component. The biodegradable coating composition further includes a minor component selected from polybutylene adipate/terephthalate, polylactic acid, and combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Taiwanese application No. 098102514, filed on Jan. 22, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a food container, more particularly to a food container that includes an inner protecting layer made from a biodegradable coating composition including polybutylene succinate.

2. Description of the Related Art

Disposable food containers are primarily made of paper and plastic. Because plastic containers are generally not biodegradable and paper can be decomposed easily and recycled, paper containers are now more popular than the plastic containers.

Referring to FIG. 1, a conventional paper cup 1 includes a paper cup body 11 with an inner surface 111 defining a receiving space 13 therein, and a protecting layer 12 coated on the inner surface 111. The protecting layer 12 is formed by coating a melted low-density polyethylene (LDPE) on the inner surface 111 of the cup body 11. Since low-density polyethylene has a softening temperature ranging from 80° C. to 101° C., and a melting point ranging from 108° C. to 110° C., and is highly resistant to chemicals and corrosion, it is suitable for use as a protection layer between the paper cup body 11 and a liquid. When hot liquid 14 is poured into the receiving space 13, the protecting layer 12 acts as a barrier between the cup body 11 and the hot liquid 14, which can prevent the hot liquid 14 from permeating into the cup body 11. However, as low-density polyethylene can not be easily decomposed in natural environment, it is not environmentally friendly.

For improvement over the aforesaid paper cup, a paper cup is coated with a protecting layer made of polylactic acid (PLA), which can be naturally decomposed. However, since polylactic acid has a glass transition temperature ranging from 58° C. to 60° C. and has poor heat resistance, the protecting layer made of polylactic acid is easily peeled off from the paper cup when hot liquid is poured into the paper cup, thereby causing the liquid to seep into and damage the paper cup.

In addition, existing methods of making a paper cup are generally carried out by coating a protecting layer on a paper sheet and by processing the coated paper sheet to form the paper cup. Therefore, when a polylactic acid coating is coated on a paper sheet, because the polylactic acid coating is relatively hard and has low adhesion strength at room temperature, it is likely to peel off during processing, thereby resulting in poor yield and hence high manufacturing costs.

In order to address the problem of polylactic acid, another improvement is to apply a surfactant on the paper cup prior to application of a polylactic acid coating so as to enhance adhesion between the paper cup and the polylactic acid coating. However, as most surfactants are toxic, when a surfactant is applied to the cup body, the surfactant can be released into the liquid received in the paper cup.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a paper container for containing food that can overcome the aforesaid drawbacks associated with the prior art.

According to the present invention, a food container comprises: a container body made of paper, and having an inner surface defining a receiving space therein, and an outer surface opposite to the inner surface; and an inner protecting layer coated on the inner surface and made from a biodegradable coating composition including polybutylene succinate as a major component.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments of this invention, with reference to the accompanying drawings, in which:

FIG. 1 is a sectional view of a conventional paper cup;

FIG. 2 is a sectional view of the first preferred embodiment of a food container according to this invention; and

FIG. 3 is a sectional view of the second preferred embodiment of a food container according to this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before the present invention is described in greater detail with reference to the accompanying preferred embodiments, it should be noted herein that like elements are denoted by the same reference numerals throughout the disclosure.

Referring to FIG. 2, the first preferred embodiment of the food container according to this invention is embodied in a cup 2. Of course, the invention may also be embodied in a box, a bowl, or a plate. The cup 2 includes a container body 21 and an inner protecting layer 22.

The container body 21 is made of paper, and has an inner surface 211 that defines a receiving space 210 therein, an outer surface 213 opposite to the inner surface 211, and an opening 212 in fluid communication with the receiving space 210.

The inner protecting layer 22 is coated on the inner surface 211 and is made from a first biodegradable coating composition including polybutylene succinate (PBS) as a major component.

It is worth mentioning that the first biodegradable coating composition may include solely polybutylene succinate for coating on the inner surface 211 of the cup 2. Alternatively, the first biodegradable coating composition may further include a minor component selected from the group consisting of polybutylene adipate/terephthalate, polylactic acid, and combinations thereof. Based on a total weight of the first biodegradable coating composition, the major component is in an amount ranging from 90 wt % to 100 wt %, and the minor component is in an amount ranging from 0 wt % to 10 wt %. By adding a small amount of polybutylene adipate/terephthalate into the first biodegradable coating composition, flowability or a melting index of the composition can be adjusted, and the viscoelasticity thereof can be increased, which improves adhesion between the inner protecting layer 22 and the container body 21. Addition of polylactic acid can increase rigidity of the inner protecting layer 22 which assists in retaining the shape of the container body 21. The weight ratio of the major component to the minor component may be varied depending on actual requirements.

Since polybutylene succinate has mechanical properties similar to those of polypropylene and acrylonitrile-butadiene-styrene copolymer (ABS), when compared to other biodegradable materials, polybutylene succinate has high mechanical strength, high heat deflection temperature (HDT) of up to about 90° C. and good waterproofing effect. Therefore, the inner protecting layer 22 made of polybutylene succinate can prevent liquid 101 received in the receiving space 210 from permeating into the container body 21. In addition, due to good heat resistance of the inner protecting layer 22, the cup 2 is not easily damaged by hot liquid. Moreover, the cup 2 is biodegradable after being disposed and thus meets environmental protection requirements.

Method of providing the inner protecting layer on the container body 21 is not limited. The container body 21 may be formed first with a predetermined shape, and then is coated with the first biodegradable coating composition so as to form the inner protecting layer 22 on the inner surface 211. Alternatively, the first biodegradable coating composition may be first coated on a paper sheet so as to form the inner protecting layer 22 thereon. Subsequently, the paper sheet having the inner protecting layer 22 is formed into the cup 2.

Referring to FIG. 3, the second preferred embodiment of the present invention differs from the first embodiment in that the cup 2 further includes an outer protecting layer 33 that is coated on the outer surface 213 and that is made from a second biodegradable coating composition including polybutylene succinate as a major component.

Likewise, the second biodegradable coating composition can include only polybutylene succinate for coating on the outer surface 213 of the cup 2. Moreover, the second biodegradable coating composition can further include a minor component selected from the group consisting of polybutylene adipate/terephthalate, polylactic acid, and combinations thereof.

When cold liquid 102 or food is placed in the receiving space 210, moisture in the atmosphere is easily condensed into water drops 103 on the outer surface 213. By virtue of the inner and outer protecting layers 22, 33, liquid 102 received within the receiving space 210 and water drops 103 on the outer surface 213 can be prevented from permeating into the container body 21.

The cup 2 may be made by first forming the container body 21 with a predetermined shape, followed by applying the first and second biodegradable coating compositions respectively onto the inner and outer surfaces 211, 213 to form the inner and outer protecting layers 22, 33. Alternatively, opposite surfaces of a paper sheet may be coated respectively with the first and second biodegradable coating compositions so as to form the inner and outer protecting layers 22, 33 thereon. Subsequently, the paper sheet having the inner and outer protecting layers 22, 33 is formed into the cup 2.

Example

A biodegradable coating composition was prepared using only polybutylene succinate that was obtained from Mitsubishi Chemical Corporation (product models: GS pla, AZ91, AZ71, and AZ61). The biodegradable coating composition including 100 wt % polybutylene succinate was coated on the inner surface 211 of the container body 21 so as to form the inner protecting layer 22.

Test of Water-Proofing Property

The cup 2 was filled with hot liquid having a temperature of 95° C., and was left to stand for 24 hours. Leakage of the hot liquid from the receiving space 210 did not occur, which indicates that the inner protecting layer 22 has good water-proofing property and good heat resistance.

Test of Adhesion

Tests were conducted according to ASTM D4541. Two paper specimens having a size of 1.5 cm×10 cm were provided. One of the paper specimens was coated with 100 wt % polybutylene succinate so as to form a protecting layer thereon, and was is labeled as A. The other paper specimen was coated with 100 wt % polylactic acid so as to form a protecting layer thereon, and was labeled as B. The two paper specimens (A and B) were stretched by applying a tensile force thereto at a speed of 300 mm/min until peeling of the protecting layers occurred. The respective tensile forces applied at the time peeling occurred were measured. The results show that the tensile forces for the specimen A range from 65 g/cm to 120 g/cm and for the specimen B range from 30 g/cm to 40 g/cm. Hence, the polybutylene succinate has a stronger adhesion property than that of polylactic acid.

With the invention thus explained, it is apparent that various modifications and variations can be made without departing from the spirit of the present invention. It is therefore intended that the invention be limited only as recited in the appended claims. 

1. A food container comprising: a container body made of paper, and having an inner surface defining a receiving space therein, and an outer surface opposite to said inner surface; and an inner protecting layer coated on said inner surface and made from a first biodegradable coating composition including polybutylene succinate as a major component.
 2. The food container of claim 1, wherein said first biodegradable coating composition further includes a minor component selected from the group consisting of polybutylene adipate/terephthalate, polylactic acid, and combinations thereof.
 3. The food container of claim 2, wherein, based on a total weight of the first biodegradable coating composition, the major component is in an amount ranging from 90 wt % to 100 wt %, and the minor component is in an amount ranging from 0 wt % to 10 wt %.
 4. The food container of claim 1, further comprising an outer protecting layer that is coated on said outer surface and that is made from a second biodegradable coating composition including polybutylene succinate as a major component.
 5. The food container of claim 4, wherein said second biodegradable coating composition further includes a minor component selected from the group consisting of polybutylene adipate/terephthalate, polylactic acid, and combinations thereof.
 6. The food container of claim 5, wherein, based on a total weight of the second biodegradable coating composition, the major component of said second biodegradable coating composition is in an amount ranging from 90 wt % to 100 wt %, and the minor component of said second biodegradable coating composition is in an amount ranging from 0 wt % to 10 wt %. 